How to return to the original appearance?

Hello, please help an experienced user. I installed the new version of Thunderbird 115.1.1 and it is completely different, especially the top part. I am installing this mail client to seniors and they don’t understand the new look and they are confused. How can I go back to the original look?
Thank you

Use the old version.

If the users who you are helping “don’t understand the new look” because it is different from the old look that they’re used to, then you have some time to start teaching them the new version and getting them used to it, before the old version becomes unsupported and stops receiving security updates.

If you’re finding that even new users don’t understand the new look because they are finding the user interface more confusing than they found the old version, then that’s feedback you should provide—the more detailed the better—to the Thunderbird team so they can try to address it in future versions. This is the wrong place to do that, since as noted above this forum is no longer being monitored by the Thunderbird team. I recommend

@Jonathan_Kamens @Deda_ladik the proper location to post is UX is for design reviews.